Our overall objective is to study mammalian neurocell differentiation and development, particularly of neuronal vs. glial cells, using various rat neural cell lines isolated from ethylnitrosourea induced tumors. Biochemical and cytological characterization of several cell lines clonally isolated from a rat peripheral neurotumor RT4 are conducted and their neuronal and glial properties examined. Particularly interesting features of the RT4 system are: a) one of the four morphologically distinct cell types is a pluripotential stem cell type which gives rise to the other three derivative cell types with a frequency of about one in one hundred thousand cells (cell-type conversion), and b) whereas the stem cell type expresses both voltage dependent Na+ influx (a neuronal property) and glial proteins, S100 and GFA (Glial Fibrillary Acidic) proteins, each of the three derivative cell types expresses either neuronal or glial properties but not both. Addition of dibutyryl cAMP in the medium stimulates further differentiation of these cell types. The cell-type conversion does not accompany any systematic change in karyotype both in chromosome number and in G-banding pattern. In this application, we propose to work on: 1) molecular biology of the mechanism of cell-type conversion (branch determination) and coordinate regulation of neuronal-glial differentiation of the RT4 cell lines, and 2) analysis of maturation processes of neuronal and glial type cell lines of RT4 under certain conditions. These studies should promote our understanding of the mechanism of the development of mammalian nervous system and also of the tumorigenesis of neurocells.